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WB UART8 Serial Communications Port

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WB UART8 Serial Communications Port Legacy documentation refer to the Altium Wiki for current information WB_UART8 Serial Communications Port This document provides detailed reference information with respect to the UART Summary peripheral device. Core Reference CR0157 (v3.1) August 01, 2008 Serial ports on embedded systems often provide a 2-wire communication channel only. The WB_UART8 is a Wishbone- compliant, serial communications port, providing serial communication with hardware handshake and FIFO buffers. The WB_UART8 can be used with any of the Wishbone-compliant processors available in Altium Designer. Features • 8-bit UART (fixed to no parity, 8 data bits and 1 stop bit) • Full Duplex • 16-byte FIFO input buffer • 8-byte FIFO output buffer • Automatic RTS/CTS hardware-controlled handshake, with user-definable watermark levels • Dedicated, high precision internal Baud rate generator • Wishbone-compliant. Available Devices The WB_UART8 device can be found in the FPGA Peripherals integrated library (FPGA Peripherals.IntLib), located in the (\Library\Fpga folder of the installation. CR0157 (v3.1) August 01, 2008 1 Legacy documentation refer to the Altium Wiki for current information WB_UART8 Serial Communications Port Functional Description Symbol Figure 1. WB_UART8 Symbol Pin Description Table 1. WB_UART8 pin description Name Type Polarity/ Description Bus size Control Signals CLK_I I Rise External (system) clock RST_I I High External (system) reset Microcontroller Interface Signals STB_I I High Strobe signal. When asserted, indicates the start of a valid Wishbone data transfer cycle CYC_I I High Cycle signal. When asserted, indicates the start of a valid Wishbone cycle ACK_O O High Standard Wishbone device acknowledgement signal. When this signal goes high, the WB_UART8 (Wishbone Slave) has finished execution of the requested action and the current bus cycle is terminated ADR_I I 4 Standard Wishbone address bus, used to select an internal register of the Wishbone slave device for writing to/reading from DAT_O O 8 Data to be sent to an external Wishbone master device (e.g. host processor) DAT_I I 8 Data received from an external Wishbone master device (e.g. host processor) WE_I I Level Write enable signal. Used to indicate whether the current local bus cycle is a Read or Write cycle: 0 = Read 1 = Write INT_O O 2/High Interrupt output lines. Two interrupts are sent to the connected host processor on this 2-bit bus. bit 0 = set High if any of the lower 4 bits of the Interrupt Status register (INTSTAT.3..INTSTAT.0) are High. These bits are all related to the transmitter. bit 1 = set High if any of the upper 4 bits of the Interrupt Status register (INTSTAT.7..INTSTAT.4) are High. These bits are all related to the receiver. 2 CR0157 (v3.1) August 01, 2008 Legacy documentation refer to the Altium Wiki for current information WB_UART8 Serial Communications Port Name Type Polarity/ Description Bus size Serial Interface Signals TXD_O O - Serial data transmit RXD_I I - Serial data receive CTS_I I Level Clear To Send. Part of the automatic hardware-controlled handshake. 0 = device connected to the WB_UART8 on the serial side is not ready to receive data 1 = device connected to the WB_UART8 on the serial side is ready to receive data. Note: If the ctsen bit in the Handshake register (HSK.0) is cleared, transmission will not depend on the readiness of the connected (remote) serial device. RTS_O O Level Request To Send. Part of the automatic hardware-controlled handshake. 0 = WB_UART8 is ready to receive data from the connected serial device. RTS_O will go Low when: • there are less bytes in the Receive Buffer than the specified low watermark in the RXLOWMARK register, or • the forcerts bit in the Handshake register (HSK.1) is High and the rtsval bit in the same register (HSK.2) is Low. 1 = WB_UART8 is not ready to receive data from the connected serial device. RTS_O will go High when: • there are more bytes in the Receive Buffer than the specified high watermark in the RXHIGHMARK register, or • the forcerts bit in the Handshake register (HSK.1) is High and the rtsval bit in the same register (HSK.2) is High. CR0157 (v3.1) August 01, 2008 3 Legacy documentation refer to the Altium Wiki for current information WB_UART8 Serial Communications Port Hardware Description Block Diagram WB_UART8 Serial Communications Port CLK_I BRG Internal Clock TXD_O Generator RST_I RTS_O SBUF Transmit Shift DAT_I[7..0] DAT_O[7..0] TRANSMIT RXD_I CTS_I ADR_I[3..0] TXLOWMARK FIFO (8 Bytes) CYC_I STB_I WE_I ACK_O SBUF Receive Shift RECEIVE RXLOWMARK FIFO (16 Bytes) RXHIGHMARK INT_O[1..0] HSK INTCTRL RXDTO STATUS INTSTATUS RST_INTSTATUS Figure 2. WB_UART8 block diagram Internal Registers The following sections detail the internal registers for the WB_UART8. Baud Rate Generator Register (BRG) Access: Read/Write The upper (BRG[23..16]), middle (BRG[15..8]) and lower (BRG[7..0]) bytes of this register are accessed separately. The register’s 24-bit value is used in the generation of the serial transmit and receive clocks. The baud rate is generated based on the overflow rate of an internal 24-bit baud rate adder. This adder increments every timer tick with the 24-bit value set in the BRG register. When the most significant bit in the adder changes state from ‘0’ to ‘1’, the baud rate counter fires. A serial bit takes 8 clock cycles from this counter. The value to be loaded into the BRG register can be calculated using the following expression: Baud Rate * 8000000h BRG = FCLK_I Note: The internal adder is not reset when the baud rate counter changes. 4 CR0157 (v3.1) August 01, 2008 Legacy documentation refer to the Altium Wiki for current information WB_UART8 Serial Communications Port Handshake Register (HSK) Access: Read/Write This 8-bit register is used to control the hardware handshake between the WB_UART8 and the remote device connected to its serial port. Table 2. The HSK register MSB LSB cts - - - - rtsval forcerts ctsen Table 3. HSK register bit functions Bit Symbol Function HSK.7 cts Returns current state of CTS_I pin when read. This bit is ignored when writing to the register. HSK.6 - Not used. Returns 0 when read HSK.5 - Not used. Returns 0 when read HSK.4 - Not used. Returns 0 when read HSK.3 - Not used. Returns 0 when read HSK.2 rtsval RTS Value bit. Controls the state of the RTS_O pin when the forcerts bit of this register (HSK.1) is High. 0 = RTS_O taken Low 1 = RTS_O taken High. HSK.1 forcerts Force RTS bit. 0 = State of RTS_O pin is purely controlled based on the number of bytes in the Receive Buffer. If the number exceeds the high watermark defined by the RXHIGHMARK register, RTS_O goes High. RTS_O will automatically go Low when the number of bytes drops below the low watermark defined by the RXLOWMARK register. 1 = State of RTS_O pin is controlled by the value of the rtsval bit of this register (HSK.2). HSK.0 ctsen Enable CTS bit. 0 = WB_UART8 is free to transmit data without regard for the current state of the CTS_I pin 1 = WB_UART8 must wait for the CTS_I pin to be taken High by the connected serial station before transmission can proceed. Status Register (STATUS) Access: Read-only This 8-bit register is used to determine the current state of the WB_UART8 device. Table 4. The STATUS register MSB LSB rxfull rxhigh rxnempty rxtimeout txshempty txlow txempty txfull CR0157 (v3.1) August 01, 2008 5 Legacy documentation refer to the Altium Wiki for current information WB_UART8 Serial Communications Port Table 5. STATUS register bit functions Bit Symbol Function STATUS.7 rxfull Receiver Full flag. Taken High if the Receive Buffer is full. STATUS.6 rxhigh Receiver High flag. Taken High if the number of bytes in the Receive Buffer exceeds the high watermark defined by the RXHIGHMARK register. STATUS.5 rxnempty Receiver Not Empty flag. Taken High if the Receive Buffer is not empty. STATUS.4 rxtimeout Receiver Time-out flag. Taken High if the Receive Buffer is not empty and has not been read within time. STATUS.3 txshempty Transmitter Shift Register Empty flag. Taken High if the Transmitter shift register is empty. STATUS.2 txlow Transmitter Low flag. Taken High if the number of bytes in the Transmit Buffer is less than the low watermark defined by the TXLOWMARK register. STATUS.1 txempty Transmitter Empty flag. Taken High if the Transmit Buffer is empty. STATUS.0 txfull Transmitter Full. Taken High if the Transmit Buffer is full. Interrupt Control Register (INTCTRL) Access: Read/Write This 8-bit register is used to enable interrupt generation for each of the corresponding bits in the STATUS register. Provided bit INTCTRL.n is High, an interrupt will be generated when the corresponding bit STATUS.n goes High. Table 6. The INTCTRL register MSB LSB rxfull rxhigh rxnempty rxtimeout txshempty txlow txempty txfull Table 7. INTCTRL register bit functions Bit Symbol Function INTCTRL.7 rxfull Enables interrupt generation for Receiver Full flag (STATUS.7). INTCTRL.6 rxhigh Enables interrupt generation for Receiver High flag (STATUS.6). INTCTRL.5 rxnempty Enables interrupt generation for Receiver Not Empty flag (STATUS.5). INTCTRL.4 rxtimeout Enables interrupt generation for Receiver Time-out flag (STATUS.4). INTCTRL.3 txshempty Enables interrupt generation for Transmitter Shift Register Empty flag (STATUS.3). INTCTRL.2 txlow Enables interrupt generation for Transmitter Low flag (STATUS.2). INTCTRL.1 txempty Enables interrupt generation for Transmitter Empty flag (STATUS.1). INTCTRL.0 txfull Enables interrupt generation for Transmitter Full (STATUS.0). Interrupt Status Register (INTSTATUS) Access: Read/Write This 8-bit register is used to reflect the state of interrupts for the WB_UART8 device.
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